Method for routing optical packets using multiple wavelength labels, optical packet router using multiple wavelength labels, and optical packet network that uses multiple wavelength labels

ABSTRACT

A method for routing optical packets using multiple wavelength labels includes converting optical packet address signals to a plurality of optical pulses having different time-deviated wavelengths by executing a first operation to impart a wavelength dependent delay time with respect to a plurality of optical pulses having different wavelengths at a same time axis position. When the optical pulses are transmitted along a predetermined optical path having dispersion, the dispersion is compensated for by executing a second operation on the optical pulses corresponding to a reverse process of the operation to impart a wavelength dependent delay time. This second operation results in the generation of a plurality of optical pulses having different wavelengths at a given point on the time axis. The pulse signals thus generated are used to determine the packet transmission route.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to optical communication by routingoptical packets using multiple wavelength labels. More particularly, thepresent invention relates to a method for routing optical packets usingmultiple wavelength labels that is based on wavelength divisionmultiplexing (WDM), to an optical packet router using multiplewavelength labels, and to an optical packet network that uses multiplewavelength labels.

2. Description of the Prior Art

In the area of optical packet communications using optical fibers,photonic networks have been proposed in which not only trunk line links,but even switching functions in network nodes connecting a plurality oftrunk lines, are implemented in the optical domain. In such a network,when each of the optical packets passes through a network node, it canautonomously switch to a predetermined route based on addressinformation carried by the packet. In this respect, there is a need foran optical packet routing system that optically labels each packet withthe respective address, checks and identifies the labels in the opticaldomain and, based on the identification result, switches the outputroute of the packet.

In prior art photonic networks based on the WDM technology, manyconfigurations and methods have been proposed in which the routinglabels are comprised as single wavelength optical signals. To identifythe packet labels, this technology uses simple wavelength identificationdevices such as arrayed waveguide gratings (AWG), which are limited withrespect to the number of labels that can be identified. Specifically,when single wavelength labels are used, with the existing level oftechnology, most networks can only handle around 100 to 200 labels, andthe upper limit for any network is around 1000.

For the processing involved, there has been proposed a label switchingrouter employing a phase code processor that uses an optical codedivision multiplexing (OCDM) system (K. Kitayama and N. Wada, “PhotonicIP Routing,” IEEE Photon. Technol. Lett., vol. 11, no. 12, pp.1689-1691, December 1999). In that system, the labels used are phaselabels having a pattern comprised of a light phase, such as 0, π, forexample, so that the labels are, for example, “000π”, “00ππ”, “0π0π,”and so forth, which are processed by a phase code processor. An inputsignal constituting a phase label is split into a plurality of signals,each of which falls incident on an independent optical correlationprocessor. Each of these optical correlation processors is configured tomatch, i.e. identify, a corresponding independent phase label. Thisdiffers from the present invention in terms of label configurationmethod and label processor.

With respect to optical encoding using time spreading/wavelength hoppingcodes, Japanese Patent No. 3038378 discloses a method in which streamsof optical pulses having different wavelengths on a bit-by-bit basis areused for encoding by setting different codes within a code sequencespecified for each channel, with decoding of received signals beingeffected by matched filtering in the time domain. This disclosurediffers from the present invention in that the disclosure does notpertain to routing.

As described above, with respect to prior art optical packet routingmethods and apparatuses, and optical packet network configurations, withcurrent technology, when single wavelength labels are used, mostnetworks can only handle around 100 to 200 labels, and the upper limitfor any network is around 1000 labels.

An object of the present invention is to provide a method for routingoptical packets using multiple wavelength labels, an optical packetrouter using multiple wavelength labels and an optical packet networkthat uses multiple wavelength labels, that enable wavelength resourcesto be effectively utilized by using wavelength division multiplexing toroute optical packets with multiple wavelength labels, thereby greatlyincreasing the number of routing labels that can be used in a networkcompared to the number of routing labels that can be used in a prior artphotonic network.

In a first aspect, the present invention achieves the above object byproviding a method for routing optical packets using multiple wavelengthlabels, the method comprising: converting optical packet address signalsto a plurality of optical pulses having different time-deviatedwavelengths by executing a first operation to impart a wavelengthdependent delay time with respect to a plurality of optical pulseshaving different wavelengths at a same time axis position and, when theoptical pulses are transmitted along a predetermined optical path havingdispersion, compensating for the dispersion by executing a secondoperation on the optical pulses corresponding to a reverse process ofthe operation to impart a wavelength dependent delay time, the secondoperation resulting in generation of a plurality of optical pulseshaving different wavelengths at a same time axis position, and usingsignals of the pulses thus generated to determine a transmission route.

In another aspect, the invention provides a method for routing opticalpackets using multiple wavelength labels, in which a predeterminedwaveband used for one-bit address signals and a one-bit data signalwaveband have identical bandwidths.

In another aspect, the invention provides a method as described in whichthe bandwidth allocated to data signals included in optical packets iswider than the bandwidth allocated to address signals.

In another aspect, the invention provides a method as described in whichaddress signals and data signals are transmitted with a predeterminedtime differential.

In another aspect, the invention provides a method as described in whichoptical packet address signals include address information that isidentified by wavelength information delimited by a predeterminedwaveband width and predetermined time differential information.

In another aspect, the invention provides a method as described in whichoptical packet address signals include first address information that isidentified by wavelength information delimited by a first wavebandwidth, and second address information that is identified by wavelengthinformation delimited by a second waveband width and predetermined timedifferential information.

In another aspect, the invention provides a method as described inwhich, based on first address information, routing is performed by afirst router that can switch optical paths according to wavelengthdifferences and, based on second address information, routing isperformed by a second router that can switch optical paths according totime differences.

In a second aspect, the invention provides an optical packet routerusing multiple wavelength labels, the router comprising: mean forseparating data signals and address signals identified by wavelengthinformation delimited by a predetermined waveband width andpredetermined time differential information included in optical packets;means for demodulating address information identified by the wavelengthinformation delimited by a predetermined waveband width andpredetermined time differential information from the address signals;means for switching an optical switch in accordance with demodulatedaddress information; and selection means that uses the optical switch toselect an optical route for the data signals.

In another aspect, the invention provides a router as described in whichthe demodulation means uses a multi-section fiber Bragg grating.

The invention also provides an optical packet router using multiplewavelength labels comprising: a pulse light source that includesmulti-wavelength laser light; means for dividing pulse signals from thepulse light source into a plurality of light paths; a means forobtaining a first pulse signal using a means that interacts with amulti-section fiber Bragg grating following modulation of one dividedpulse signal; a means for obtaining a second pulse signal comprisingmeans for narrowing waveband width of other divided pulse signals andmeans for modulating the reduced-bandwidth pulse signals; means foradjusting a time differential between the fist pulse signal and thesecond pulse signal; and means for guiding the first and second pulsesignals thus adjusted to a same light path.

In a third aspect, the invention provides an optical packetcommunication network that uses multiple wavelength labels, the networkincluding a plurality of routers that can switch optical paths inaccordance with differences in combinations of multiple optical pulsewavelengths and time differentials included in address signals, with atleast two of the routers being connected together.

In another aspect, the invention provides an optical packetcommunication network that uses multiple wavelength labels, the networkincluding a first router that can switch optical paths in accordancewith differences in wavelengths of multiple optical pulses included inaddress signals, and a second router that can switch optical paths inaccordance with differences in combinations of multiple optical pulsewavelengths and time differentials included in address signals, with thesecond router being connected to the first router.

Further features of the invention, its nature and various advantageswill be more apparent from the accompanying drawings and followingdetailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing showing the configuration of a multiple wavelengthlabel switching router system.

FIG. 2 shows an example of a first configuration of an optical packethaving a multiple wavelength label.

FIG. 3 shows an example of a second configuration of an optical packethaving a multiple wavelength label.

FIG. 4 shows an example of a third configuration of an optical packethaving a multiple wavelength label.

FIG. 5 shows an example of the configuration of a network that usesmultiple wavelength switching routers and wavelength routers.

FIG. 6 illustrates a method of generating multiple wavelength labelsusing a multi-section fiber Bragg grating.

FIG. 7 illustrates a method of matching multiple wavelength labels usinga multi-section fiber Bragg grating.

FIG. 8 is a block diagram of a multiple wavelength packet transmitterthat transmits optical packet signals having multiple wavelength labels.

FIG. 9 is a block diagram of part of a multiple wavelength labelswitching router that uses an array of multi-section fiber Bragggratings to process the multiple wavelength labels.

FIG. 10 shows signal waveforms of each part of a multiple wavelengthlabel switching router, in which FIG. 10(a) shows the detected signalwaveform of a multiple wavelength label generated by means of amulti-section fiber Bragg grating; FIG. 10(b) shows the detected signalwaveform of the packet consisting of a header having a multiplewavelength label and a payload data; FIG. 10(c) shows the detectedwaveform of a signal signing a label match output by a multiplewavelength label matching unit comprised of a multi-section fiber Bragggrating; FIG. 10(d) shows the detected waveform of a signal signifying alabel non-match output by a multiple wavelength label matching unitcomprised of a multi-section fiber Bragg grating; FIG. 10(e) shows thedetected waveform of a signal output by a three-port switch signifying aport #1 multiple wavelength label; and FIG. 10(f) shows the detectedwaveform of a signal output by a three-port switch signifying a port #3multiple wavelength label.

FIG. 11 shows an example of a multiple wavelength label switching routernetwork.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the prior art packet communications, a packet signifies the temporalpropagation of signal system sets. However, in the case of the presentinvention, a packet signifies the wavelength propagation, or bothwavelength and temporal propagation, of signal system sets. The presentinvention relates to the handling of codes having structural elements inthe form of a plurality of points in two-dimensional space that arepropagated in terms of wavelength and temporal direction. In particular,the invention uses as optical labels optical signal system data that arepropagated in terms of both wavelength and time-based direction. Usingthese optical labels as identifiers in optical domain packet switchingmakes it possible to effectively utilize wavelength resources by greatlyincreasing the number of labels that can be used within a singlenetwork. Details are explained in the following embodiments.

FIG. 1 shows the configuration of a multiple wavelength label switchingrouter system. The router comprises a label/data separator 1, a multiplewavelength label processor 2, a label converter 3, an optical switch 4,an optical delay unit 5 and an optical coupler 15. Transmitted opticalpackets, each carrying multiple wavelength labels affixed to data asheader information, are input to the router. These packets are separatedinto two by the label/data separator 1 and the respective parts sent tothe label processor 2 and optical delay unit 5. In the label processor2, the labels are not converted to electrical signals, but are read intheir native optical signal form, resulting in the output of a switchcontrol signal. The control signal is sent to the optical switch 4,where an optical wave detector converts it to a high-frequency signalthat is applied to the optical switch 4. The optical delay unit 5applies a time delay to data going to the optical switch 4, the timedelay corresponding to the difference between that optical path and theoptical path to the label processor 2. Following this, the opticalswitch 4 outputs a signal based on a control signal from the labelprocessor 2. The optical coupler 15 combines this output with a newlabel output from the label converter 3, and outputs the result as anoptical packet.

FIG. 2 shows an example of a first configuration of an optical packetwith a multiple wavelength label. These optical packets are divided intowavebands λ1, λ2, . . . λn. In the following, this is referred to as alarge-band configuration. Each of the wavebands in this large-bandconfiguration is further subdivided into what is referred to assmall-band configurations. These small-band configurations are assumedto have bands A, B, C, D, E, for example. Address information in smallbands is mapped into a multiple wavelength pulse train to effect opticallabelization. Of the small bands A, B, C, D, E, bands A to D are usedfor multiple wavelength labels and the remaining small band E isallocated for the transmission data signals, to thereby produce theoptical packets. If a large-band label uses 8 waves, this labelgeneration method makes it possible to ensure over 10000 labels.

FIG. 3 shows an example of a second configuration of an optical packetwith a multiple wavelength label. As in the first example, these opticalpackets are divided into large bands λ1, λ2, . . . λn. To form opticalpackets, in a small-band configuration a small band is allocated to eachof the optical pulses used for each optical label that has a differentcenter wavelength from the data signals, and all of the remaining bandswithin a large-band member are allocated for the data signal.

FIG. 4 shows an example of a third configuration of an optical packethaving a multiple wavelength label. Here, the fill bandwidth of each ofthe bands λ1, λ2, . . . λn is used for address information for thelabel. Also, data signals are generated using the full bandwidth of alarge-band member. In this case, the label and data portions can bereadily separated using a time gate or the like. An advantage of thisconfiguration is that it makes it possible to easily increase the ratioof data signal to address signal.

FIG. 5 shows the arrangement of a network using the above multiplewavelength label switching routers. The network of FIG. 5 is configuredwith multiple wavelength label optical packet sender-receivers 7connected to multiple wavelength label switching routers 8 that arelinked by commercially available wavelength routers 9. A single-wavelength-packet sender-receiver 22 can also be connected to thewavelength router 9. Also, as shown in FIG. 11, a network can be formedof multiple wavelength label switching routers 8 connected together. Inthe packet routing method of this invention, the wavelength router 9routes packets on a large-band configuration member basis, with thesmall bands within each large-band configuration member being regardedas having the same wavelength. However, the multiple wavelength labelswitching router 8 identifies down to the small-band configuration levelin performing routing based on the multiple wavelength label processor 2and optical switch shown in FIG. 1. This configuration can be readilymerged with a photonic network that uses conventional single-wavelengthrouting.

In the configurations described with reference to FIGS. 2, 3 and 4, whenlarge-band members are divided into small-band members, the small-bandmembers each have a different center wavelength. FIG. 6 shows an exampleof generation of multiple wavelength labels in the form of a string ofoptical pulses arrayed along the time axes thereof. As shown in FIG. 6,labels can be generated with a time differential by projecting multiplewavelength pulses onto a multi-section fiber Bragg grating and applyingto the reflected pulse signals a time delay that differs in accordancewith the wavelength.

FIG. 7 shows a multiple wavelength label discriminator based on amulti-section fiber Bragg grating. The multi-section fiber Bragg gratingshown in FIG. 6 has a configuration that is inverted with respect to thedirection of light incidence. When specified multiple wavelength labelsfall incident on this label discriminator, the reflected signals areadjusted to compensate for the time delay received by each pulse duringlabel generation, to thereby reproduce the original multiple wavelengthpulses. When the label discriminator finds that the combinedcharacteristic (wavelength and time-position) of a reflected band doesnot match that of an incident label, no compensation is effected for thetime delay received at the time the label was generated, so the originalpulses are not reproduced. Thus, it becomes possible to distinguishbetween matching and non-matching labels by subjecting the output of thelabel discriminator to threshold processing. The multiple wavelengthlabel processor shown in FIG. 1 can be configured with an array ofmulti-section fiber Bragg grating based label discriminators. Opticalpackets that simultaneously fall incident on the array can then besimultaneously processed using a routing table and packet labels toassign predetermined routes and labels.

FIG. 8 is a block diagram of a multiple wavelength packet transmitterthat transmits optical packet signals having multiple wavelength labels.In FIG. 8, a supercontinuum light source 10 denotes a multiplewavelength light source with a center wavelength of 1.56 μm. This lightsource produces light pulses with a broad wavelength distribution. Thelight pulses emitted by the light source 10 pass through an opticalcoupler 17 a and a bandpass filter 16 with a 5-nm bandpasscharacteristic. Light pulses transmitted by the bandpass filter 16 forma small-band member constituting a data signal, and light pulses thatare not transmitted by the bandpass filter 16 form a group of small-bandmembers constituting a multiple wavelength label. By means of anintensity modulator 12 b, the optical signals passed by the filter 16are intensity-modulated by a 10-Gbps electrical signal generated by apattern generator 11 b and time-adjusted by the optical delay unit 5 toform burst data. Light that does not go to the filter 16 isintensity-modulated by an intensity modulator 12 a, using a 10-Gbpselectrical signal generated by a pattern generator 11 a, and is input toa multi-section fiber Bragg grating 13 connected to the light path by acirculator 14, to thereby form a multiple wavelength label. The burstdata and multiple wavelength label are combined by an optical coupler 17b and output as an optical packet.

FIG. 9 is a block diagram of a part 21 of a multiple wavelength labelswitching router that uses an array of three multi-section fiber Bragggratings 13, each having a different characteristic, to process themultiple wavelength labels. Optical packets having multiple wavelengthlabels that are input to the router are divided by an optical coupler 17a into a label portion that does not pass through the bandpass filter16, and a data portion that does not go to the bandpass filter 16. Thelight is divided into a plurality of beams by the optical coupler 17 a,with each beam going via a circulator 14 to fall incident on amulti-section fiber Bragg grating 13. Label matching is performed usingthe multi-section fiber Bragg grating system shown in FIG. 7. When thereis a label match, the label discriminator outputs a switch operationcontrol signal that opens a specific gate switch, allowing the emissionof data-section signals from a selected port.

FIG. 10 shows the waveforms of signals from the multiple wavelengthpacket transmitter of FIG. 8 that are input to the router shown in FIG.9. FIG. 10(a) shows the signal waveform of a multiple wavelength labelgenerated by means of a multi-section fiber Bragg grating; FIG. 10(b)shows the signal waveform of the packet consisting of a header having amultiple wavelength label and a payload data; FIG. 10(c) shows thewaveform of a signal signifying a label match output by a multiplewavelength label matching unit comprised of a multi-section fiber Bragggrating; FIG. 10(d) shows the waveform of a signal signifying a labelnon-match output by a multiple wavelength label matching unit comprisedof a multi-section fiber Bragg grating; FIG. 10(e) shows the waveform ofa signal output by a three-port switch signifying a port #1 multiplewavelength label; and FIG. 10(f) shows the waveform of a signal outputby a three-port switch signifying a port #3 multiple wavelength label.This method of the present invention for routing optical packets usingmultiple wavelength labels, enables problem-free routing of opticalsignals.

The invention having the configurations described in the foregoingembodiments and aspects provides the following effects. It readilyenables routing to be carried out in an optical packet communicationsystem, using labels comprised of multiple wavelength optical pulses.The fact that optical pulses in a two-dimensional space defined bywavelength and time axes are used as the basic address signals greatlyincreases the number of labels that can be used for routing purposes.Moreover, these address signals can be readily generated by means of asimple configuration that uses multi-section fiber Bragg gratings,facilitating the generation of packet routing labels and the routingitself. The optical packet router of the invention can also be used inconjunction with a conventional packet routing system that switchespaths based on wavelength differences. Networks can also be configuredwith optical packet routers of the invention connected together.

1. A method for routing optical packets using each of multiplewavelength labels, comprising: executing on each packet a firstoperation to impart a wavelength dependent delay time to a plurality ofoptical pulses having different wavelengths at a same time axisposition, said first operation resulting in conversion of optical packetaddress signals to a plurality of optical pulses having differentwavelengths and having deviated time axis positions; transmitting theplurality of optical pulses along a predetermined optical path and, whenthe optical path has dispersion, compensating for said dispersion;executing a second operation on the optical pulses corresponding to areverse process of said first operation, said second operation resultingin generation of a plurality of optical pulses having differentwavelengths at a same time axis position; and using signals of theplurality of optical pulses thus generated to determine a transmissionroute.
 2. The method according to claim 1, in which a predeterminedwaveband used for one-bit address signals and a one-bit data signalwaveband have identical bandwidths.
 3. The method according to claim 1,in which a bandwidth allocated to data signals included in the opticalpackets is wider than a bandwidth allocated to the address signals. 4.The method according to claim 1, in which data signals and the opticalpacket address signals are transmitted with a predetermined timedifferential.
 5. The method according to claim 1, in which the opticalpacket address signals include address information that is identified bywavelength information delimited by a predetermined waveband width andpredetermined time differential information.
 6. The method according toclaim 1, in which the optical packet address signals include firstaddress information that is identified by wavelength informationdelimited by a first waveband width, and second address information thatis identified by wavelength information delimited by a second wavebandwidth and predetermined time differential information.
 7. The methodaccording to claim 6, in which, based on the first address information,routing is performed by a first router configured to switch opticalpaths according to wavelength differences and, based on the secondaddress information, routing is performed by a second router that canswitch optical paths according to time differences.
 8. An optical packetrouter using each of multiple wavelength labels, comprising: means forseparating an optical packet into data signals and address signals, saidaddress signals including optical pulses having different wavelengthsand being identified by wavelength information delimited by apredetermined waveband width and predetermined time differentialinformation included in optical packets; means for demodulating addressinformation delimited by the wavelength information from the addresssignals to obtain demodulated address information; means for switchingan optical switch in accordance with the demodulated addressinformation; and selection means that uses the optical switch orselecting an optical path for the data signals.
 9. The router accordingto claim 8, in which the demodulation means uses a multi-section fiberBragg grating.
 10. An optical packet router using each of multiplewavelength labels, comprising: a pulse light source that includesmulti-wavelength laser light; means for dividing pulse signals from thepulse light source into a plurality of light paths; means for obtainingfirst pulse signals using a multi-section fiber Bragg grating followingmodulation of some divided pulse signals; means for obtaining secondpulse signals comprising means for reducing waveband width of otherdivided pulse signals and means for modulating the pulse signals withreduced bandwidths; means for adjusting a time differential between thefirst pulse signals and second pulse signals; and means for guiding thefirst and second pulse signals thus adjusted to a same light path.